Photographic elements exhibit sensitivity to a wide variety of light and radiation wavelengths. Elements based on silver halides, for example have a natural or intrinsic sensitivity to blue light. Silver halide can also be sensitive to other wavelengths, ranging from X rays, ultraviolet, various portions of the visible spectrum, and infrared radiation. This can be accomplished through various known means, such as varying the halide content (e.g., silver chloride is primarily sensitive to ultraviolet radiation) or through the use of various spectral sensitizing dyes. Because most silver halide is naturally sensitive to blue light, and because of sensitivity imparted to silver halide through chemical sensitization, spectral sensitization, or both, photographic elements must usually be handled in the dark from the time they are prepared until after they are exposed and processed.
The requirement for dark handling can be satisfied in a number of ways, such as darkroom handling, packaging the element in a light-sealed cassette or other container, and safelight handling, where the wavelength of the safelight is selected so as to not overlap with the sensitivity of the element. These techniques have proven very useful over time, but they are subject to disadvantages. Darkroom handling is cumbersome, time-consuming, expensive, and subject to exposure of the element if the darkroom is dark conditions of the room are compromised. Cassettes and containers are expensive, difficult to prepare, require a mechanism for allowing the element to be exposed at the right time and place, and are subject to failure if not properly sealed to light. Safelights can also be useful, but their feasibility depends on a photographic element having little or no spectral sensitivity in the range of light emitted by the safelight. Since many sensitizing dyes sensitize silver halide in regions of the spectrum in addition to that for which they are intended, the feasibility of using safelights is often quite limited. Also, safelights must be used in conjunction with a darkroom to be effective.
In an effort to avoid the above problems, and to provide photographic materials handleable in white light or room light, several specialized materials have incorporated filter dye layers above the radiation sensitive layers. Such dyes must effectively absorb radiation that would otherwise reach the radiation sensitive layer from the time the element is prepared until it is exposed and processed. The dye must also be decolorized and/or removed from the element during processing, so as to not adversely effect image quality or cause dye stain. For example, U.S. Pat. No. 3,705,807 describes a radiographic material that is handleable under yellow safelights having a protective layer comprising a yellow absorbing filter dye. U.S. Pat. No. 4,232,116 describes an ultraviolet-sensitive photographic film that comprises a yellow filter layer over a silver halide emulsion layer of at least 50 mole % silver chloride.
The use of filter dye layers over radiation sensitive layers to impart white light or safelight handleability to photographic elements has been limited to relatively specialized situations for a number of reasons. One problem has been that many potential water soluble filter dyes tend to wander throughout the photographic material, causing a number of adverse effects, such as desensitization, fogging, stain, and others. Water insoluble filter dyes are much less susceptible to wandering, are usually not decolorized or removed during photographic processing. One solution to this dilemma has been to coat soluble filter dyes along with a polymeric mordant to reduce dye wandering. This approach, however, has only limited effectiveness as mordants tend to either bind the dye too strongly, resulting in incomplete dye removal and dye stain, or too weakly, resulting in dye wandering and its associated adverse effects. Furthermore, at the levels of dye concentration often required for white light or safelight protection, these problems are often aggravated.
It is known in the art to use filter dyes for other purposes. Lemahieu et al describe in U.S. Pat. No. 4,092,168 a combination of specific monomethine oxonol and pentamethine oxonol dyes useful as antihalation dyes. The dyes are insoluble at coating pH's, thus eliminating the need for a dye mordant, and are soluble for removal and/or decolorization at processing pH's. These dyes are disclosed as being dispersible as solid particles in aqueous hydrophilic colloid compositions; however, no suggestion is given that any other dyes might possess the same beneficial solubility properties. The reference discusses the absorbance properties of the dyes and their suitability for antihalation use, but no teaching whatsoever is presented that the dyes might be useful at the levels required for white light or safelight protection nor is there any teaching as to what other dyes might possess the beneficial solubility properties of being aqueous insoluble at coating pH's and highly aqueous soluble at processing pH's. There is also no teaching that would enable anyone as to how to choose dyes other than those specifically disclosed in the U.S. Pat. No. 4,092,168 to obtain those properties.